Medical evaluations typically rely on a variety of tests for determining physiological conditions of patients. One common test is known as electrolyte analysis. This test determines the percentages of several ionized minerals in samples of blood taken frown patients. These ionized minerals include calcium, sodium, and potassium. Other tests can determine the pH value of the blood as well as other physiological indicators. The blood samples are typically collected in sampling syringes. The samples taken from the patients often consist of about three milliliters of blood. Them are a number of sampling syringes known in the art for drawing and holding samples for testing.
The samples of blood typically are moved to laboratories for testing and analysis shortly after being obtained from the patients. Testing preferably should occur within 30 minutes or less of the samples being drawn. Dissolved gases in the blood begin diffusing from the samples immediately. The blood begins to coagulate and bind the minerals in the fluidal blood together. Coagulation skews the test results because the bound minerals resist detection during the analysis which only detects the free ionized minerals in the fluidal blood. If some of the minerals are clotted out of the fluid, the analysis results in a false determination of mineral content percentages less than is actually present in the blood of the patients being tested. Such incorrect determinations can lead to mis-diagnosis, which may lead to injury to the patients.
To reduce test interference caused by coagulation, sampling syringes typically include anticoagulants. The anticoagulants delay the coagulation of the blood and provide a larger window of time after drawing samples of blood to begin testing. The anticoagulant commonly used in sampling syringes is a compound known as heparin. Heparin is typically supplied in the form of a lyophilized powder or a liquid. The heparin is placed in a sample-holding chamber of a sampling syringe. The liquid blood drawn from the patient into the sampling syringe dissolves or dilutes the heparin. The heparin reduces the coagulation of the blood for a period of time, which period provides time to transfer the sampling syringe to a laboratory for analysis of the sample of blood.
Typically, the heparin is supplied in the form of a salt. Various metal salts of heparin are known, including lithium salt of heparin, calcium salt of heparin, and zinc salt of heparin. These metals are cations which may bind with the heparin at anion binding sites. It is considered that in solution the cations continuously dissociate from and re-associate with the anion binding sites on the heparin molecule, and reach a state of equilibrium with the other cations in the fluidal blood sample. These cations compete for the anion binding site depending on their respective binding affinities and proportionate concentrations while the heparin performs the anticoagulation function.
These metals have varying affinity for binding to the heparin. Zinc binds more strongly with heparin than calcium which binds more strongly than lithium. These differences in binding affinity of the cation and the anion have an impact on the analysis of the blood sample. The particular, studies show that the analysis of blood containing a zinc salt of heparin detects an increased amount of ionized calcium in the blood sample over that detected in a control sample of blood, possibly by detecting the dissociated zinc as ionized calcium. In contrast, studies show that the analysis of blood containing a lithium salt of heparin detects a decreased amount of ionized calcium in the blood sample, possibly due to the ionized calcium occupying the anion binding sites on the heparin molecule which are vacated by the dissociated lithium and the associated calcium is undetected by the analyzer. The particular salt of heparin accordingly effects the perceived amount of ionized calcium in contrast to the actual amount as indicated by a control sample. Also, due to variances in the raw material used to manufacture the heparin molecule, the heparin has varied potencies. Each batch of a salt of heparin is tested and a certificate that accompanies the packaged heparin salt sets forth the determined USP potency. Such differences may lead to incorrect diagnosis of the physiological condition of the patient. Misdiagnosis may lead to incorrect treatment or failure to treat, to the possible injury of the patient.
Accordingly, there exists a need in the art for a heparin anticoagulant which substantially eliminates a skew in a determined amount of ionized calcium imparted by the heparin in the blood samples and an improved method of blending a salt of heparin for use as an anticoagulant.